The Wood Library-Museum

Engstrom Model 150

Anesthesiologists may use muscle relaxant drugs to provide good operating conditions during surgery. While in this state, the patient's breathing is done for him or her by the anesthesiologist. Introduced in 1942, the use of muscle relaxants increased over the next decades, often becoming part of general anesthesia. The growing need for ventilation during anesthesia coincided with the world-wide spread of poliomyelitis, or polio. Thousands of polio survivors needed a respirator of their own to be able to breathe. Anesthesiologists sought a way to reduce the complication of this additional equipment in the operating room.

Swedish physician Carl Gunnar Engstrom, M.D. (1912-1987) filed to patent a new respirator in 1950. Four years later, the Engstrom Universal Respirator, also called the Model 150, was introduced. It was the first mechanical ventilator that could also deliver inhalation anesthetics. Like the Emerson Respirator, it applied both positive and negative pressure to the patient’s lungs, but did this more gradually. Mechanical ventilators soon became a standard feature of all anesthesia machines, improving patient safety. This example of the Engstrom Respirator has been modified by the addition of a Draeger Vapor halothane vaporizer.

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